Known inboard boat drive systems comprise a steering and propulsion unit arranged under the water, which can pivot about a vertical axis. Propulsion is produced by one or more propellers, whose rotation axis can be pivoted by means of the steering unit. Pivoting of the propulsion vector results in a steering action for the boat. The propulsion and steering unit comprises a vertically arranged column which accommodates the driveshaft for the propellers and which passes through a bottom plate, also called the connecting piece, that is set into the hull of the boat. Especially in the case of motor yachts, the steering and propulsion unit determines the draft of the vessel and, when the vessel runs aground or a collision with underwater objects occurs, is therefore particularly exposed and at risk. It is known, when fixing the steering and propulsion unit to the hull, to provide predetermined break-points for example in the form of calibrated screw-bolts, so that if subjected to an impact of more than a defined severity the steering and propulsion unit will break away from the hull without the formation of a leak at the fracture points. A problem can arise, however, if after breaking away the steering and propulsion unit is flung backward, i.e. in the aft direction, and at the same time upward against the underside of the boat's hull. When struck by the sharp-edged propeller the hull can be damaged and a leak produced.